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Create Disposable

This pattern is helpful when you want to do something temporarily and then restore some state. This was inspired by the System.Disposable.Disposable() class defined in System.Core.dll distributed by the Reactive Extensions for .NET (Rx) library.

Implementing IDisposable

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open System
let createDisposable f =
    {
        new IDisposable with
            member x.Dispose() = f()
    }

Example: printing in the console with different colors

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let changeColor color () = 
    let current = Console.ForegroundColor
    Console.ForegroundColor <- color
    createDisposable (fun () -> Console.ForegroundColor <- current)

let red = changeColor ConsoleColor.Red
let green = changeColor ConsoleColor.Green

using (red()) (fun _ ->  printfn "This is red : %A" [1 .. 3])
using (green()) (fun _ -> printfn "This is %A : %A" ConsoleColor.Green [1 .. 3])

namespace System

val createDisposable : f:(unit -> unit) -> IDisposable

Full name: Script.createDisposable

val f : (unit -> unit)

type IDisposable =
member Dispose : unit -> unit

Full name: System.IDisposable

val x : IDisposable

IDisposable.Dispose() : unit

val changeColor : color:ConsoleColor -> unit -> IDisposable

Full name: Script.changeColor

val color : ConsoleColor

val current : ConsoleColor

type Console =
  static member BackgroundColor : ConsoleColor with get, set
  static member Beep : unit -> unit + 1 overload
  static member BufferHeight : int with get, set
  static member BufferWidth : int with get, set
  static member CapsLock : bool
  static member Clear : unit -> unit
  static member CursorLeft : int with get, set
  static member CursorSize : int with get, set
  static member CursorTop : int with get, set
  static member CursorVisible : bool with get, set
  ...

Full name: System.Console

property Console.ForegroundColor: ConsoleColor

val red : (unit -> IDisposable)

Full name: Script.red

field ConsoleColor.Red = 12

val green : (unit -> IDisposable)

Full name: Script.green

field ConsoleColor.Green = 10

val using : resource:'T -> action:('T -> 'U) -> 'U (requires 'T :> IDisposable)

Full name: Microsoft.FSharp.Core.Operators.using

val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

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More information

Link:	http://fssnip.net/34
Posted:	13 years ago
Author:	Cesar Mendoza
Tags:	idisposable , disposable , patterns